The present invention relates to orthopedic surgical devices and, in particular, it concerns devices for moving joints while maintaining traction across the joint.
It is known to employ traction across a joint in the treatment of intra-articular fractures. Especially where the bones are fragmented to an extent which precludes direct surgical procedures to stabilize the fragments, traction is known to induce ligamentotaxis in which the fragments re-align due to forces on their ligamentous and volar plate attachments.
Traction across a fractured joint can be applied by pushing apart pins implanted in each of the adjacent bones. An example of a simple system for applying traction in this manner is the "S Quattro Flexible Mini External Fixator" commercially available from Surgicraft Ltd., England.
It has been found, however, that prolonged application of traction across a fractured joint without movement of the joint frequently results in loss of joint mobility due to irregular re-molding of the joint surfaces and soft tissue scarring (fibrosis). A number of attempts have therefore been made to develop traction systems which permit freedom of movement of the joint, referred to as "dynamic traction" systems.
One approach to dynamic traction is set out in an article entitled "The Dynamic Traction Method: Combining Movement and Traction for Intra-Articular Fractures of the Phalanges" by Robert R. Schenck, MD (Hand Clinics 10 (2) May 1994). This describes a system in which rubber bands are mounted between a transosseous wire located in the distal head of the middle phalanx and an external frame. In the primary example, the frame is formed as a large loop in the plane of movement of the joint. The point of connection of the rubber bands can then be slid manually around the loop to flex the joint while maintaining the applied traction. Also discussed are adaptations of existing continuous passive motion devices to apply tension, also by use of rubber bands.
A particular shortcoming of the dynamic traction systems discussed by Schenck is the imprecision and inconvenience of adjustment of the tension applied. Adjustment is achieved primarily by adding or removing rubber bands, thereby giving large discrete jumps in the amount of tension. Although a possibility of twisting the rubber bands is mentioned, no mechanism is provided for such an adjustment. The systems also require professional supervision and demand a high degree of patient compliance and cooperation, making them unsuitable for home-treatment.
A second approach to dynamic traction systems is represented by a proximal interphalangeal joint hinge commercially available under the tradename Compass from Smith & Nephew Richards Inc., USA. This hinge is secured by five pins drilled into the bones. Once positioned, an adjustment screw allows distraction of the joint. Once the desired degree of distraction is achieved, the pin blocks are fixed in position relative to the hinge. It is not possible to achieve a precise and measurable amount of traction. During normal operation of the hinge, no flexibility or elasticity is exhibited.
Although the Compass system provides effectively continuously variable adjustment of the degree of distraction of the joint, the lack of flexibility in the system causes other shortcomings. Firstly, the hinge is extremely sensitive to misalignment. For this reason, a superfluous axial pin is drilled into the bone for alignment of the hinge. However, even with the extra pin, sufficiently precise positioning of the hinge is difficult to achieve. Additionally, even within the operative range of accuracy, a slight misalignment of the hinge may result in a large variation in the distraction of the joint during movement. In such circumstances, the lack of flexibility may cause extreme variations in the force applied to the joint, either in over-traction or compression, potentially resulting in severe damage to the joint. Finally, passive movement of the joint is achieved by labor intensive manual operation of a worm-gear mechanism which demands a high degree of patient compliance.
There is therefore a need for a dynamic traction device for treatment of intra-articular fractures which applies traction elastically across the joint in a manner so as to render slight misalignments non-critical. It would also be advantageous to provide devices for aiding the accurate alignment of such a device.